Toner fuser system having post-fuser media conditioner

ABSTRACT

A toner fuser system suitable for producing high quality color transparencies is provided. The fuser system includes a media conditioning assembly located directly downstream of a fuser assembly, which may be a roll fuser or an instant-on belt fuser. The conditioner assembly includes a convective heat source, a heating zone, and a convective circulation path past the heat source and the heating zone to provide convective heat transfer to a transparency in the heating zone. A transparency (or other media) with toner to be fused travels on a media path first through the fuser assembly and then through the heating zone of the conditioner assembly. The fuser assembly causes toner to adhere to the transparency just well enough to allow the transparency to pass into the conditioner. In the conditioner, the toner is reheated, thereby causing the surface of the toner to reflow into a smooth, glossy, and uniform surface that increases light transmission efficiency of color transparencies. Additionally, the system eliminates the need for silicone oil, which is used in some prior art systems to prevent sticking of the transparency to the fuser assembly.

BACKGROUND OF THE INVENTION

In electrophotographic (EP) printers and copiers, an image formed fromdeveloped thermoplastic toner is transferred to media such as paper,cardstock, labels, or transparencies. The toner is then fused to adherethe toner to the media. Current EP printers and copiers generally employone of two types of fuser systems to adhere the toner to the media: aroll fuser system or an instant-on belt fuser system. Both fuser systemsuse a combination of temperature and pressure to melt and bond thethermoplastic toner either into the fibers of the paper or, in the caseof transparencies, onto the surface of the film.

The first type of fuser system, the roll fuser system, comprises tworolls, of which either one or both has an elastomeric coating. Usuallythe bottom roll, typically known as the back-up roll (BUR), is springloaded into the top roll, or hot roll (HR), although rolls with fixedcenters are also used to create interference between the two rolls. TheHR is the roll that contacts the unfused toner. The spring load, orinterference in the case of fixed centered rolls, along with theelastomeric coating creates a nip, an area of high pressure andtemperature that serves as the working area of the fusing system. Thetime that the media spends in the nip is known as the residence time ordwell time and is determined by the nip width and process speed of themedia. Heat is typically provided by a lamp such as a halogen type lamp.The lamp is usually placed inside the HR, although it may be placed inboth rolls or only in the BUR.

The second type of fuser system, the instant-on belt fuser system,comprises a polyamide belt, sometimes called a sleeve, and a softsilicon-coated back-up roll that are pressed together at a particularpressure to form a nip. This system may be an idling-belt system, inwhich the back-up roll is driven by a drive mechanism and the beltidles, or a driven-belt system, in which the belt is driven by a drivemechanism and the back-up roll idles. The belt in this system is thin,typically 0.10 mm or thinner. This system is called an “instant-on”fuser, because the thin belt wraps directly over the heating element,typically a ceramic type, at the nip, whereby the fuser reachesoperating temperatures very quickly due to the lack of thermal massbetween the heating element and media.

The roll fuser system is well known and in wider use than the instant-onbelt fuser system. However, it has a few inherent drawbacks, especiallyin color EP applications. One problem with roll fusers is associatedwith the geometry of the rolls. In order to achieve acceptable fusegrade at faster speeds, a larger nip is needed to meet the requiredresidence times. A common way to make the nip larger is to make therolls larger. As the exit radius of curvature is increased, however, therelease of the media from the surface of the hot roll becomes moredifficult; there is a point at which the beam strength of the media isnot great enough to overcome the adhesion force of the toner against thehot roll and the media follows the roll rather than properly releasingfrom the roll. Multi-colored prints are even more difficult to releasedue to the added pile height associated with mixing of the toner to makenon-primary colors. Added pile height increases the tendency for thetoner and therefore the media to stick to the hot roll.

A typical solution to prevent sticking of the media to the hot roll isto add silicone oil to the hot roll, thus providing a weak boundarylayer between the toner and the hot roll. Another advantage of siliconeoil is that the weak boundary layer results in a smooth toner surface,which results in glossy images on paper and, more importantly, vibrantcolors when projecting transparencies. Silicone oil, however, hasseveral disadvantages. When oiled sheets are duplexed, oil istransported back through the machine, which may be detrimental to the EPprocess. Oil supply items can significantly increase the printed costper page. The oil supply such as an oil roll, web, or oil bottle must beroutinely replaced by the user, typically every five-to twenty-thousandsheets. Oil can leave a spotty residue on the sheet, and in the case oftransparencies, residual oil can cause the sheets to stick together.Minimizing the quantity of oil metered to the printed sheet ischallenging, because it is difficult to ensure consistent oil flow inall situations.

The belt fuser system is advantageous over the roll fuser system in thatit allows for a sharp exit angle, which helps the release of the mediafrom the belt without the need for silicone oil. The sharp release angleis formed either by wrapping the belt around a fairly sharp portion ofthe heater housing or allowing the belt to slacken at the exit portion.The beam stiffness of the media can thereby overcome the tendency of themedia to follow the belt. The toner surface, however, is left rough,resulting in a matte finish and a non-translucent transparency thatresults in non-vibrant or ‘muddy’ looking colors when projected. This‘muddy’ appearance is caused by scattering of the projector light by thenon-flat toner surface.

Another disadvantage of the roll fuser system is the slower processspeed needed for color transparencies. Because the optical properties ofcolor transparencies are critical, the toner layers must be well mixedand the surface of the toner must be optically smooth with little or novoids and irregularities. To meet these requirements, the process speedfor transparency fusing is slowed, so that the residence time can beincreased and therefore more heat can be transferred to the toner. Thepaper-to-transparency speed ratio for color EP printers is typically 3or 4 to 1, but some machines have ratios as high as 11 to 1. Also, thefuser temperature is increased so that the energy transferred to thetransparency is much greater than for paper applications. Otherdisadvantages of the roll system compared to the instant-on belt fusersystem are that warm-up time is longer and temperature swings aregreater.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a post-fuser media conditioning systemoperative in conjunction with a toner fuser assembly for anelectrophotographic printer. In the fuser assembly, toner is initiallyfused by heat and pressure. Toner is then fully fused by convectiveheating in the post-fuser media conditioner.

The post-fuser media conditioning system comprises a conditionerassembly comprising an insulated heating chamber, a convective heatsource, and a heating zone located within the heating chamber. Aconvective circulation path is provided within the heating chamber pastthe heat source and the heating zone to provide convective heat transferto media in the heating zone. A media path is provided through theheating zone of the conditioner assembly.

The post-fuser media conditioner of the present invention allows for theelimination of silicone oil from the color EP fusing process. The fuserassembly may be a roll fuser or an instant-on belt fuser, which allowsthe advantages of either system to be chosen, as desired. The presentinvention achieves a significant increase in the fusing speed of colortransparencies relative to a similar sized fuser with oil. A similarsized fuser with the post-fuser media conditioner may increase the speedat least three-fold and yet still achieve vibrant color transparencies.The transparency speed is a function of the post-fuser mediaconditioner's ability to transfer heat to the toner. In a furtherembodiment, the post-fuser media conditioner provides a mechanism tochange parameters that effect the surface properties of the toner,allowing users to adjust the toner gloss on paper according to theirpreference.

DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the following drawings in which:

FIG. 1 schematically illustrates a first embodiment of a post fusermedia conditioner according to the present invention;

FIG. 2 illustrates a second embodiment of a post fuser media conditioneraccording to the present invention; and

FIG. 3 illustrates a third embodiment of a post fuser media conditioneraccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a fuser system incorporating a fuser assembly 12 anda post-fuser media conditioner assembly 14 according to the presentinvention. The fuser assembly 12 may utilize a roll fuser, an instant-onbelt fuser, or any other type of fusing system. The media conditioner 14comprises an insulated, convective heating chamber 16 located downstreamof the fuser assembly 12. A media transport mechanism 18 to carry mediathrough the conditioner and a heat source 20 are located within thechamber 16. The fuser assembly causes toner on the media to adhere tothe media just well enough to allow the media to pass into theconditioner without sticking to the fuser assembly. The media passesthrough a heating zone in the chamber. While the media is in the heatingzone, the heat source 20 heats the toner sufficiently to cause itssurface to reflow into a smooth, glossy, and uniform surface. A suitablecontroller 22 is provided to control the fuser assembly and mediaconditioner.

The heating chamber 16 is formed to withstand the temperature of theheat source and to retain as much heat as possible. For example, thechamber may be formed of a casing 24 of metal, such as aluminum, coveredor coated with one or more layers 26 of a thermally insulative material.A further outer layer of an insulative plastic material (not shown) ispreferably provided as well. A layer of heated air (not shown) may alsobe provided for insulation.

A media entrance 30 is provided in one side of the heating chamber 16adjacent the fuser assembly 12, and a media exit 32 is provided in theopposite side. The media is fed from the fuser assembly 12 directly intothe post-fuser media conditioner 14. The distance d between the fuserassembly and the media conditioner is minimized to retain the maximumamount of heat in the media before entering the conditioner. An entranceguide 34 and an exit guide 36 may be used to direct media from the fuserassembly 12 into the conditioner 14. The media transport mechanism 18within the chamber 16 transports media through the chamber from theentrance to the exit. The transport mechanism may be a transport belt 38within the heating zone, as illustrated in FIG. 1, or any other suitablestructure, such as rollers. Alternatively, the fuser assembly may pushthe media through the heating zone in the chamber. Additionally oralternatively, the media may be picked up by rollers outside of theheating zone.

The convective heat source 20 in the chamber may comprise, for example,one or more quartz heater bulbs, one or more halogen bulbs, a resistanceheater assembly, or re-circulated heated air from the fuser assembly. Acombination of different heat sources may also be used, such asrecirculated heated air from the fuser assembly in combination with aquartz or halogen bulb. A shield plate 40 is preferably provided betweenthe heat source 20 and the media path 42 through the heating zone toprevent radiant energy from impinging on the media, because radiantenergy is unevenly absorbed by the different colors of toner. An opening44 or vent in front of the shield plate 40 near the media entrance 30allows air to circulate down to the media path. Preferably, acirculation path that allows air to recirculate past the heat source,indicated by dashed arrows 46, is provided. A blower assembly 48, suchas a fan, may also be provided to assist in the circulation of as muchheat as possible. Circulation of air maximizes system efficiency bymaximizing heat transfer to the media and minimizing heat loss throughthe exit.

Media that passes through a fuser assembly is typically not flat.Non-flat media must be able to pass through the conditioner 14 withoutjamming or allowing the soft toner to contact any portion of theconditioner that might cause smearing. Also, down side duplexed sheetsare toner covered and thus when in the conditioner, the soft tonercontacts the transport assembly of the conditioner, if present. Thetoner must not be damaged when this occurs, and the transport assemblyof the conditioner must not become contaminated with toner or paper jamsmay occur. For these reasons, the transport assembly of the conditionermay utilize a ribbed transport belt, star wheels, a cooled surface, or alow surface energy surface that resists toner contamination, such as aPTFE or VITON® coating. Alternatively, the conditioner may bedeactivated when the printer is utilized in duplex mode, which wouldresult in matte-finished duplex jobs. For example, the heat source inthe conditioner may be turned off. In this case, the blower assembly 48preferably continues to run to provide a faster cool down. Additionally,the conditioner may be movable to move out of the media path. Similarly,another media path may be provided outside of the conditioner.

The fuser assembly 12 and media conditioner 14 are controlled by anysuitable controller 22. Under control of the controller, the fuserassembly causes the toner to adhere to the transparency just well enoughto allow the media to pass into the conditioner. The media conditionerreheats the toner after it passes through the fuser, causing the surfaceof the toner to reflow into a smooth, glossy, and uniform surface. Thissmoothing effect increases the light transmission efficiency of thecolor transparencies. By underfusing the toner in the fuser pass, therisk of hot offsetting is minimized and also energy consumption isminimized. The underfusing and subsequent conditioning are controlled bya suitable controller. The degree of fusing is determined by theparameters of time, temperature, and pressure in the fuser orconditioner and the type of toner. The pressure and time in the fuserassembly are preset during manufacture of the fuser assembly and themedia conditioner. The temperature for underfusing the toner is thendetermined as a function of these parameters and the type of toner, aswould by understood by those of skill in the art, and is controlled bythe controller. A typical temperature range may be 140 to 210° C.

The entire system is encased in order to maximize the efficiency of thesystem, which promotes low energy consumption as well as minimizing thetemperature gradient of the system. The air flow at the media surfaceinterface is made to be turbulent for optimal heat transfer to thetoner. For example, the fan speed may be set sufficiently high and/orbaffles may be provided to increase collisions with the air molecules orchannel the airflow through a smaller area before impinging on the mediaon the transport assembly. In general, the design of the post-fusermedia conditioner attempts to maximize efficiency and minimize theenvelope size or volume, while producing smooth, uniform toner surfacesthat exhibit high gloss and excellent light transmission.

The invention solves the problems associated with silicone oil asdescribed above. Other advantages of this system include highertransparency throughput since the media conditioner gives the toner itsgood optical properties. The cost per page is lower, because an oilsupply does not need to be replaced. Less customer interaction is neededwith the machine due to the lack of an oil supply. No oil residue isleft on media.

Also, in a further embodiment, the media conditioner allows a user theoption of choosing the gloss on the media through the operator panel bychanging the media conditioner's parameters of temperature and speed ofthe media through the conditioner. For example, a user may choose thedegree of gloss on a control panel, and the controller then sets thetemperature and speed appropriate to the chosen degree of gloss. Ingeneral, the greater the temperature is in the conditioner and theslower the media passes through the conditioner, the greater the glosslevel on the media.

FIG. 2 shows another embodiment of the present invention, in which thepost-fuser conditioner is more closely integrated with the fuserassembly. The fuser assembly and the media conditioner are preferablycontained in a single housing. Media passes through the fuser assembly112 and into a heating zone 119. A heat source 120 is provided in theinterior of a blower assembly 148 in a region above the media pathdefined by a casing 124, which is preferably insulated. A baffle 150directs the circulation of heated air toward the media path whileblocking radiant energy from impinging on the media. The transportassembly includes a plate 152 upon which the media slides as it passesthrough the media conditioner. The fuser assembly 112 is sufficientlyclose to the media conditioner 114 to push media through the mediaconditioner on the plate 152. The plate may be adjustable to accommodatedifferent media paths, if desired. For example, the plate is mounted inslots in opposed interior sidewalls of the chamber (only one slot 154 isshown). A second set of slots (only one slot 156 is shown) is providedat a different level to allow adjustment of the level of the plate, ifdesired.

A still further embodiment is illustrated in FIG. 3, in which a postfuser media conditioner 214 is mounted to the housing of a fuserassembly 212. Media passes through the fuser assembly and into a heatingzone 219 in the conditioner 214. A heat source 220 and blower assembly248 are provided inside a casing 224. Baffles 250 direct the circulationof heated air toward the media, while blocking radiant energy fromimpinging on the media. The transport assembly includes a plate 252 uponwhich the media slides as it passes through the heating zone 219 in themedia conditioner. A transport roll assembly 253 outside of the casing224 assists in pulling the media through the conditioner.

It should be appreciated that other embodiments having differentconfigurations of the media conditioner components, the transportassembly, the heat source, the blower, and the shield plate or plates,may be provided.

We claim:
 1. A toner fuser system for an electrophotographic printercomprising: a fuser assembly comprising a pressure application regionand a heat source located to heat the pressure application region; amedia conditioner assembly comprising a convective heat source and aheating zone and at least one shield plate located to block radiant heatfrom the convective heat source from entering the heating zone and aconvective circulation path past the convective heat source and theheating zone to provide convective heat transfer to media in the heatingzone; and a media path including an upstream portion through thepressure application region of the fuser assembly and a downstreamportion through the heating zone of the media conditioner assembly. 2.The toner fuser system of claim 1, wherein the media conditionerassembly further comprises an insulated heating chamber, and theconvective heat source and the heating zone are located within theinsulated heating chamber.
 3. The toner fuser system of claim 2, whereinthe insulated heating chamber further includes a layer of heated gas. 4.The toner fuser system of claim 3, wherein the layer of heated gascomprises recirculated heated gas from the fuser assembly.
 5. The tonerfuser system of claim 1, wherein the convective heat source includes aquartz heater bulb, a halogen bulb, or a resistance heater, orrecirculated heated gas from the fuser assembly.
 6. The toner fusersystem of claim 1, wherein the convective heat source includes a quartzheater bulb, a halogen bulb, or a resistance heater, and the convectiveheat source further includes recirculated heated gas from the fuserassembly.
 7. The toner fuser system of claim 1, wherein the mediaconditioner assembly further includes a blower mechanism located in theconvective circulation path to assist circulation of gas heated by theconvective heat source.
 8. The toner fuser system of claim 7, whereinthe convective heat source is located within the blower mechanism. 9.The toner fuser system of claim 1, wherein the media conditionerassembly further includes a transport mechanism configured to transportthe media through the heating zone on the media path.
 10. The tonerfuser system of claim 9, wherein the transport mechanism comprises atransport belt or rollers.
 11. The toner fuser system of claim 10,wherein the transport belt comprises a ribbed belt.
 12. The toner fusersystem of claim 9, wherein the transport mechanism includes a cooledsurface.
 13. The toner fuser system of claim 9, wherein the transportmechanism includes a low surface energy surface.
 14. The toner fusersystem of claim 9, wherein the fuser assembly forms at least a portionof the transport mechanism operative to push media through the mediaconditioner assembly.
 15. The toner fuser system of claim 9, wherein thetransport mechanism includes a plate within the heating zone.
 16. Thetoner fuser system of claim 15, wherein the plate is adjustably locatedwithin the heating zone.
 17. The toner fuser system of claim 9, whereinthe transport mechanism is located at least partially in the heatingzone.
 18. The toner fuser system of claim 9, wherein the transportmechanism is located downstream of the heating zone.
 19. The toner fusersystem of claim 1, wherein the fuser assembly comprises an instant-onbelt fuser.
 20. The toner fuser system of claim 1, wherein the fuserassembly comprises a roll fuser.
 21. The toner fuser system of claim 1,wherein the media conditioner assembly and the fuser assembly arelocated in a common housing.
 22. The toner fuser system of claim 1,further comprising a controller in communication with the fuser assemblyand the media conditioner assembly.
 23. The toner fuser system of claim22, wherein the controller is operative to control the temperature ofthe convective heat source and the speed of the media on the media path.24. A post-fuser media conditioning system operative in conjunction witha toner fuser assembly for an electrophotographic printer, comprising: aconditioner assembly comprising an insulated heating chamber, aconvective heat source, and a heating zone located within the insulatedheating chamber, and at least one shield plate located to block radiantheat from the convective heat source from entering the heating zone, anda convective circulation path within the insulated heating chamber pastthe convective heat source and the heating zone to provide convectiveheat transfer to media in the heating zone; and a media path through theheating zone of the conditioner assembly.
 25. The post-fuser mediaconditioning system of claim 24, wherein the convective heat sourceincludes a quartz heater bulb, a halogen bulb, or a resistance heater.26. The post-fuser media conditioning system of claim 24, wherein theconditioner assembly further includes a blower mechanism located on theconvective circulation path to assist circulation of gas heated by theconvective heat source.
 27. The post-fuser media conditioning system ofclaim 26, wherein the convective heat source is located within theblower mechanism.
 28. The post-fuser media conditioning system of claim24, wherein the conditioner assembly further includes a transportmechanism configured to transport the media through the heating zone onthe media path.
 29. The post-fuser media conditioning system of claim28, wherein the transport mechanism comprises a transport belt orrollers.
 30. The post-fuser media conditioning system of claim 28,wherein the transport mechanism includes a cooled surface or a lowsurface energy surface.
 31. The post-fuser media conditioning system ofclaim 28, wherein the transport mechanism further includes a plate. 32.A method of fusing toner to media in an electrophotographic printer,comprising: providing media with unfused toner thereon; in a firstfusing operation, passing the media through a region of high pressureand high temperature to cause the unfused toner to partially fuse to thesurface of the media; and in a second fusing operation, passing themedia through a convective heating zone downstream of the first fusingoperation, blocking radiant energy from impinging on the media in theheating zone, to cause the partially fused toner to fully fuse to thesurface of the media.
 33. The method of claim 32, further comprising inthe second fusing operation, providing a blower to assist circulation ofheated gas past the heating zone.
 34. The method of claim 32, furthercomprising repeating the first fusing operation and the second fusingoperation on a second side of the media.
 35. The method of claim 32,wherein in the media providing step, the media comprises a transparency.36. The method of claim 32, wherein in the media providing step, thetoner comprises colored toner.
 37. The method of claim 32, wherein thefirst fusing operation comprises controlling the temperature and time ofthe media in the region of high pressure and high temperature to achievea desired degree of partial fusing.
 38. The method of claim 32, whereinthe second fusing operation comprises controlling the temperature andtime of the media in the convective heating zone to achieve a desireddegree of fusing.
 39. The method of claim 32, wherein the second fusingoperation further comprises adjusting the temperature and time of themedia in the convective heating zone to achieve a desired degree oftoner glossiness on the media.